Solvent extraction of coal by a heavy oil

ABSTRACT

A SOLID CARBONACEOUS MATERIAL, SUCH AS COAL, IS CONVENTED TO LIQUID PRODUCTS AND THE ASPHALTENE CONTENT OF A HEAVY HYDROCARBONACEOUS LIQUID IS REDUCED IN A PROCESS WHEREIN THE SOLID IS SOLVENT EXTRACTED BY THE LIQUID AND THE RESULTANT MIXTURE OF LIQUIDS IS RECOVERED AS THE PRODUCT.

United States Patent Office 3 ,705,002? Patented Dec. 5, 1972 Int. Cl. Cg 1/04 US. Cl. 208-8 6 Claims ABSTRACT OF THE DISCLOSURE A solid carbonaceous material, such as coal, is converted to liquid products and the asphaltene content of a heavy hydrocarbonaceous liquid is reduced in a process wherein the solid is solvent extracted by the liquid and the resultant mixture of liquids is recovered as the product.

BACKGROUND OF THE INVENTION This invention relates to a process for the conversion of carbonaceous materials, such as coal, to liquid products. More particularly, this invention relates to a process for the conversion of coal to a liquid product by solvent extraction of the coal using a heavy hydrocarbonaceous liquid containing heptane-insoluble material, and recovery of the mixture of the solvent and liquified coal as the product of the process.

Reserves of solid carbonaceous substances such as coal, lignite, oil shale, etc., represent a valuable source of raw materials for the production of liquid hydrocarbon products commonly obtained from petroleum. The relative abundance of sources of solid carbonaceous materials with respect to those of petroleum, makes the use of these solids to supplement and replace petroleum as energy sources economically desirable.

Several processes for converting coal to valuable liquid products are known to the art. Recently, high pressure hydrogenation and solvent extraction techniques have been developed, the latter of which is related to the process of this invention. In the processes of solvent extraction known to the prior art, crushed, finely-divided particulate coal, or other carbonaceous material, is placed in contact with a liquid solvent which dissolves a part of the solid, usually in the presence of hydrogen gas. Following the contact, the liquid solvent and the liquified part of the solid are separated from the remaining solid material by filtration, centrifuging or a similar operation. In the processes known to prior art, the previously solid material is separated from the solvent, typically by fractional distillation, and is further processed by conventional hydrocarbon processing techniques such as coking, cracking, hydrogenation, etc., to convert the solvent extracted material into more useful products. 1

One of the problems encountered in the solvent extraction method of liquifying solid carbonaceous substances is the non-selective nature of the solvation which takes place. The process is intended to extract the most valuable, hydrogen-rich fraction of the solid. But sol-Vents which are elfective in extracting this hydrogen-rich fraction also liquify an undesirable fraction containing asphaltenes. Asphaltenes are undistillable compounds of carbon of high molecular weight, and contain less than about 7% hydrogen by weight. Asphaltenes are also insoluble in normal heptane. They are present not only in the products from solvent extraction of carbonaceous materials such as coal, but also in petroleum crude oil and fractions thereof such as topped or reduced crude oils, heavy cycle stocks visbreaker liquid effluent and the bottoms from atmospheric crude towers. The asphaltenic fractions of all these liquid hydrocarbons are of little intrinsic value and interfere with the processing of the more valuable heavy oil fractions with which they are mixed. Thus, the reduction of the asphaltenes content in any processable hydrocarbon liquid is a desirable improvement thereof.

SUMMARY OF THE INVENTION The objective of this invention is to originate an efficient method for the conversion of solid carbonaceous materials to valuable liquid products and the simultaneous improvement of the properties of a heavy hydrocarbon liquid. More specifically, the object of this invention is an eflicient method for the solvent extraction of valuable liquids from solid carbonaceous materials and the simultaneous conversion of a part of a heavy hydrocarbon liquid from a less desirable material to a more desirable material. The particular object of this invention is the elficient solvent extraction of a valuable fraction of a solid carbonaceous material with a concurrent reduction in the asphaltenes contained in a heavy hydrocarbon liquid.

As hereinabove set forth, these objects are accomplished through the utilization of a heavy asphaltene-containing hydrocarbonaceous liquid as the solvent in a process for the solvent extracting of solid carbonaceous materials. Therefore in one embodiment the present invention provides a process for the simultaneous liquefaction of a solid carbonaceous material and reduction of the asphaltenes content of a heavy hydrocarbon which comprises, first, placing the solid carbonaceous material, in a particulate state, in contact with the heavy hydrocarbon liquid under solvent extraction conditions, wherein the heavy liquid is utilized as the solvent, and, second, separating the mixture of liquified material and solvent from the remaining solid material, thereby recovering as the synthetic product a liquid composed of the liquified carbonaceous material and of heavy hydrocarbon solvent, the asphaltenes content thereof having been reduced in the process.

In the preferred embodiment of my invention, comminuted coal is introduced into a solvent extraction Zone Where it is admixed with a petroleum crude oil in the presence of hydrogen gas and at a temperature and pressure which will produce a liquefaction of a part of the coal.

Subsequently, the liquid mixture is separated from the remaining solid coal by centrifugation and filtration. The liquid mixture as thus recovered is suitable for processing as a petroleum crude oil would be, and is enriched in that the asphaltenes content of the solvent is diminished in the process and the asphaltenes content of the liquified coal is lower than that obtained in the processes used in the prior art.

The solid carbonaceous material utilized in the process of the present invention may be any sort of coal, lignite, oil shale, tar sand, or similar substance. The liquid hydrocarbonaceous solvent utilized in the solvent extraction may be any heavy hydrocarbon substance which is liquid at the solvent extraction conditions, contains asphaltenes that are insoluble in normal heptane, and of which boils above about 650 F. and 50% of which boils above about 1,000 F. The solvent and solid may be admixed in any weight ratio but a Weight ratio from about 1 part solvent to 1 part solid up to about 5 parts solvent to 1 part solid is preferred.

In the preferred embodiment of the present invention, the solid carbonaceous substance is a bituminous coal having a high content of volatile material. Typically, a high content of volatile material would be about 20% or higher volatiles in the moisture and ash free coal. The

coal is subjected to the extraction conditions in a finelydivided state. Said finely-divided state is well-exemplified by coal particles which pass through about a 200 mesh or finer Tyler sieve.

The liquid hydrocarbonaceous solvent utilized in the preferred embodiment of the present invention is a heavy whole crude oil. Typical of the preferred solvent is a Cold Lake crude oil having an A.P.I. gravity of about and containing a fraction of materials insoluble in normal heptane of about 8%. The crude oil, used as the solvent in the preferred embodiment, contains sufiicient heavy oils such that at least 80% of the crude boils above 650 F. and 50% boils above 1,000 F.

In a general embodiment of the present invention, the admixed solvent and solid are subjected to sufficient temperature and pressure, in the presence of hydrogen gas, to liquify the desired fraction of the solid. The solvent extraction process may be conducted in either a batch or a continuous reaction vessel. Solvent extraction conditions include a temperature of about 55 F. to about 935 F. and a pressure of about 500 p.s.i.g. to about 10,000 p.s.i.g. Hydrogen gas is present at the above-indicated pressure.

Preferably, the mixture of solvent and solid is processed in a continuous reaction vessel at a flow rate which results in a liquid hourly space velocity of about 0.75 to about 5, where the liquid hourly space velocity is defined as the volumetric flow of the feed per hour divided by the volume of the reactor. The hydrogen gas is recycled to the process from the reactor effiuent at a rate of about 5,000 to about 10,000 standard cubic feet per barrel of combined solvent and solid, and hydrogen gas is added to the reaction at a rate sufficient to maintain the above stated range of pressures.

ter the solvent and solid have been exposed to the solvent extraction conditions for a length of time sufficient for the desired fraction of the solid to have been liquified, the mixture of solvent, liquified previously solid material and the remaining solid is withdrawn and the remaining solid is separated from the product of the process, which product is the combined solvent and liquified previously solid material. The separation may be etfected by filtration, centrifugation or any other effective means.

In the preferred embodiment of the present invention, the above described, finely-divided, solid bituminous coal is admixed with the above described heavy petroleum crude oil solvent at a weight ratio of four parts crude oil to one part solid coal. This mixture of coal and crude oil forms the feed to a reaction zone, wherein the solvent extraction conditions of this preferred embodiment are maintained. The solvent extraction conditions of the preferred embodiment include a temperature of about 850 F. and a hydrogen gas pressure of about 3,000 p.s.i.g. The feed to the reaction zone is continuously passed through the reaction zone at a rate sufiicient to maintain a liquid hourly space velocity of about 0.5 based on the volume of the feed. Hydrogen gas is recycled to the reaction zone from the reaction zone efiluent at a rate of about 15,000 standard cubic feet per barrel of the feed to the reaction zone. The solvent extraction conditions should be maintained so as to produce a conversion of the solid coal to a liquid extract of about 70% by weight of the moisture-and ash-free coal.

When the feed to the reaction zone has been subjected to said solvent extraction conditions, it is collected as the efiluent from the reaction zone. During the period that the feed was subjected to the solvent extraction conditions, about of the solid coal will have been liquified to form valuable hydrocarbon products and a part of the crude oil solvent, which was insoluble in normal heptane, will have been converted into a material which is soluble in normal heptane. The solids in the eflluent from the reaction zone are separated from the liquids in the effiuent from the reaction zone by centrifugation and subsequent filtration. The liquids in the eflluent from the reaction zone are recovered as the product from the process.

The hydrocarbons recovered from the process of the present invention constitute a synthetic crude oil which can be processed in the same manner as any common petroleum crude oil. Both the component derived from the solid and the component derived from the solvent are improved from the process of this invention in that the content of asphaltenes i reduced in both. This reduction in asphaltenes in the synthetic crude oil, particularly with respect to the component derived from the solid, renders the resulting hydrocarbon more readily processable than is the hydrocarbon obtained in the solvent extraction processes known to prior art.

The process of the present invention makes possible the elimination of the step in the usual processes of solvent extraction known to prior art, in which the solvent is separated from the liquified solid and recycled to the feed to the reaction zone. The elimination of the above said step is particularly noteworthy in that it eliminates a part of the heating of the liquified carbonaceous material, reducing the possibility of its repolymerization and the consequent difliculties in processing.

I claim as my invention:

1. A process which comprises solvent extracting a hydrocarbonaceous solid with a heavy asphaltene-containing petroleum oil at a temperature of from about 55 F. to about 935 F. and a hydrogen pressure of from about 500 p.s.i.g. to about 10,000 p.s.i.g. to liquify at least a portion of said solid and reduce the asphaltene content of said oil, and recovering the resultant liquid product.

2. The process of claim 1 further characterized in that at least about by volume of said oil boils above about 650 F.

3. The process of claim 2 further characterized in that at least about 50% by volume of said oil boils above about 1,000 F.

4. The process of claim 1 further characterized in that said solid is coal.

5. The process of claim 1 further characterized in that said solvent is a petroleum crude oil fraction.

6. The process of claim 1 further characterized in that said oil is a whole petroleum crude oil.

References Cited UNITED STATES PATENTS 6/ 1971 Gatsis 2088 7/1970 Gatsis 208-8 

